Track and Sprocket Drive for Drilling

ABSTRACT

A drilling rig includes a mast base and a mast having a structural frame extending from the mast base. The structural frame includes a first track extending along the length of the structural frame and a second track extending along the length of the structural frame spaced from and parallel to the first track. The drilling rig also includes a top drive carriage assembly having at least one sprocket arrangement operatively engaged with one of the first track and the second track. The first track and the second track each include a plurality of bushings equally spaced apart and attached to spaced apart track plates. The at least one sprocket arrangement has a plurality of teeth configured to operatively engage the plurality of bushings such that the top drive carriage assembly moves along the length of the structural frame of the mast.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Patent Application No. 61/148,582 entitled “Track and Sprocket Drive for Drilling” filed Jan. 30, 2009, which is hereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates, in general, to a drilling rig primarily for use in gas drilling and, more particularly, to a drive mechanism for a carriage of the drilling rig.

2. Description of Related Art

A vertical drilling rig is commonly used in oil, gas, and coal bed methane well drilling. Conventional vertical drilling rigs use heavy drill pipe and/or drill collars in order to exert downward force on the drill bit as it enters the earth's surface and begins the well bore.

Vertically drilling an oil or gas well begins with the step of positioning a drill string terminating with a drill bit and rotating the drill string such that the drill bit bores into the ground or into the seabed, in the case of offshore drilling, until it reaches a predetermined depth or penetrates a petroleum-bearing or gas-bearing geological formation. The components of the drill string, such as the drill pipe and/or drill collars, are threaded for interconnection. The uppermost length of drill pipe in the drill string is connected to a top drive positioned on a carriage. As the drill bit advances and the top of the drill string approaches the working platform or drill floor of the drilling rig, additional lengths of drill pipe must be added to the drill string in order to advance the well further into the ground. This is accomplished by temporarily supporting the top of the drill string near the drill floor level, disconnecting the top drive from the top of the drill string, and then lifting a new section of drill pipe into position using the rig's elevating system and screwing it into the top of the drill string. The top drive is then reconnected to the drill string, and drilling operations resume until it is again necessary to add drill pipe. In addition, as the drill bit of the vertical drilling rig drills deeper below the earth's surface, it is sometimes necessary to apply force in the opposite direction of the drilling direction (pull-back force) in order to prevent placing too much weight on the drill bit and causing damage to or failure of the drill bit. This is accomplished by using the top drive.

It is also known in the art to drill oil, gas, and methane wells in a vertical direction initially and then deviate or turn the well bore in increments toward a horizontal direction as the drill bit reaches the target formation. The bore hole is then continued in the horizontal direction for a distance. This method exposes a greater volume of the oil, gas, or methane producing formation to the well bore and produces a higher and longer producing well.

In order to convert a vertical drilling rig to accomplish the combination vertical-horizontal drilling, it is necessary that the vertical drilling rig include a top drive to provide rotational force to the drill pipe, rather than a rotary table and Kelly bar. Top drive units are typically driven by either hydraulic or electric power. The top drive is supported by the rig's main hoist and moves downward along with the drill string as drilling progresses. The top drive also provides thrust and pull-back forces which are needed while drilling in the horizontal direction. The top drive typically travels along vertical guide rails built into the mast of the rig superstructure. However, the distances of the horizontal runs produced by conventional devices and methods are limited by the capability of the top drive to apply thrust and pull-back forces to the drill pipe. The diameters of the horizontal runs are also limited by the ability to apply thrust and pull-back forces to the drill pipe. There are several known drive mechanisms for allowing the top drive to travel along the mast of a rig superstructure, thereby applying thrust and pull-back forces to the drill pipe. However, each of these known drive mechanisms suffers from various deficiencies.

For instance, U.S. Pat. No. 7,318,491 to Riel discloses a modified horizontal directional drilling (HDD) assembly. The modified HDD assembly includes a rotary and carriage assembly. The rotary and carriage assembly is adapted to move along a thrust frame and provide thrust force, pull-back force, and rotational torque to a drill pipe or casing. The rotary and carriage assembly is driven by a positive rack and pinion carriage system. Such rack and pinion systems generally lose efficiency as the gear teeth and guide system wear. The pressure angle of the gear teeth results in forces acting to spread the pinion away from the rack. These forces must be counteracted by the bearings on the pinion drive, as well as by any guide system used to maintain distance between pinion shaft and rack. As the guide system and gear teeth wear, the effective pressure angle typically increases, thereby increasing the load on the pinion bearings and guide system. The increased load results in decreased efficiency due to increased drag. In addition, if one of the teeth in the rack becomes inoperative due to wear, the entire rack may need to be replaced.

United States Patent Application Publication No. 2007/0246264 to Folk is directed to a worm and collar drive drilling rig. The drilling rig includes a substructure and a mast. The mast includes a worm drive which is a driveshaft having a helical groove cut into its surface. A collar having means for engaging the worm drive is driven longitudinally along the length of the worm drive by rotation of the worm drive. In its simplest form, the collar may be a nut having an internal thread complementary to the worm drive helical groove. The collar includes a plurality of rollers disposed internally which engage the worm drive. The rollers are arranged in a helical manner within the collar, which matches the helical pitch of the worm drive. Each roller includes a shaft and a head which is rotatably supported on the shaft by a suitable bearing set. The roller shaft passes through an opening in the collar and is secured by a nut. However, this system suffers from various deficiencies. For instance, it is complex and expensive to manufacture. In addition, if the worm drive malfunctions or wears out, it is difficult to replace.

Accordingly, a need exists for a drive system to allow a top drive carriage to travel along the mast of a drilling rig in an efficient manner and that allows for easy replacement and repair of damaged parts.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a drive system for a top drive carriage that precisely and efficiently moves the top drive carriage along a mast. The mast may include multiple sections that are easily assembled in the field. Another object of the present invention is to guide the top drive carriage without the use of additional guide rails. In addition, it is a further object of the present invention to provide a drive system for a top drive carriage that allows for easy replacement and repair of damaged parts.

The present invention is directed to a drilling rig that includes a mast base and a mast having a structural frame extending from the mast base. The structural frame includes a first track extending along the length of the structural frame and a second track extending along the length of the structural frame spaced from and parallel to the first track. The drilling rig also includes a top drive carriage assembly having at least one sprocket arrangement operatively engaged with one of the first track and the second track. The first track and the second track each include a plurality of bushings equally spaced apart and attached to spaced apart track plates. The at least one sprocket arrangement has a plurality of teeth configured to operatively engage the plurality of bushings such that the top drive carriage assembly moves along the length of the structural frame of the mast.

Each of the plurality of bushings may be attached to the spaced apart track plates by a bolt and nut arrangement. In addition, each of the first track and the second track may further include wear plates positioned adjacent to the plurality of bushings to prevent wear on the track plates. At least one first roller configured to move with the top drive carriage assembly may be provided adjacent to an outer edge of the spaced apart track plates of the first track, and at least one second roller configured to move with the top drive carriage assembly may be provided adjacent to an outer edge of the spaced apart track plates of the second track.

The at least one sprocket arrangement may be driven by a planetary gear arrangement driven by a hydraulic motor. The top drive carriage assembly may include four sprocket arrangements. Two of the sprocket arrangements may be operatively engaged with the first track and two of the sprocket arrangements may be operatively engaged with the second track. Each of the sprocket arrangements may be driven by a separate planetary gear arrangement driven by a hydraulic motor. The sprocket arrangement may be manufactured using a water-jet technique. The drilling rig may further include a control panel having speed control mechanisms for controlling the hydraulic motors.

In addition, the present invention is also directed to a drive mechanism for a top drive carriage assembly of a drilling rig. The drive mechanism includes a track having a plurality of bushings equally spaced apart and attached to spaced apart track plates; and at least one sprocket arrangement operatively engaged with the track. The at least one sprocket arrangement includes a plurality of teeth configured to operatively engage the plurality of bushings such that the sprocket assembly moves along the track.

Each of the plurality of bushings may be attached to the spaced apart track plates by a bolt and nut arrangement. In addition, the track may further include wear plates positioned adjacent to the plurality of bushings to prevent wear on the track plates. The at least one sprocket arrangement may be driven by a planetary gear arrangement driven by a hydraulic motor. The sprocket arrangement may be manufactured using a water jet technique.

The present invention is also directed to a method of drilling. The method includes the step of providing a drilling rig. The drilling rig includes a mast base and a mast having a structural frame extending from the mast base. The structural frame includes a first track extending along the length of the structural frame and a second track extending along the length of the structural frame spaced from and parallel to the first track. The drilling rig also includes a top drive carriage assembly having at least one sprocket arrangement operatively engaged with one of the first track and the second track. The first track and the second track each include a plurality of bushings equally spaced apart and attached to spaced apart track plates. The at least one sprocket arrangement has a plurality of teeth configured to operatively engage the plurality of bushings such that the top drive carriage assembly moves along the length of the structural frame of the mast. The method also includes the steps of: raising the mast onto the mast base such that it is substantially perpendicular to a surface; coupling an upper end of a drill string having a drill bit at a lower end thereof to a top drive drill head of the top drive carriage assembly; and providing a rotational drive force to the drill string by the top drive drill head such that the drill bit is rotated to bore into the earth.

Each of the plurality of bushings may be attached to the spaced apart track plates by a bolt and nut arrangement. In addition, each of the first track and the second track may further include wear plates positioned adjacent to the plurality of bushings to prevent wear on the track plates. At least one first roller configured to move with the top drive carriage assembly may be provided adjacent to an outer edge of the spaced apart track plates of the first track, and at least one second roller configured to move with the top drive carriage assembly may be provided adjacent to an outer edge of the spaced apart track plates of the second track. The at least one sprocket arrangement may be driven by a planetary gear arrangement driven by a hydraulic motor. The top drive carriage assembly may include four sprocket arrangements. Two of the sprocket arrangements may be operatively engaged with the first track and two of the sprocket arrangements may be operatively engaged with the second track.

These and other features and characteristics of the present invention, as well as the methods of operation and functions of the related elements of structures, will become more apparent upon consideration of the following description and the appended claims with reference to the accompanying drawings, all of which form a part of this specification, wherein like reference numerals designate corresponding parts in the various figures. As used in the specification and the claims, the singular form of “a”, “an”, and “the” include plural referents unless the context clearly dictates otherwise.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a drilling rig having a top drive carriage assembly driven by a track and sprocket drive mechanism in accordance with the present invention;

FIG. 2 is a front plan view of a portion of the drilling rig of FIG. 1;

FIG. 3 is a portion of the front plan view of the drilling rig of FIG. 1 enlarged for magnification purposes;

FIG. 4 is a cross-sectional view of the top drive carriage assembly taken along line 4-4 in FIG. 2;

FIG. 5 is a portion of the view of FIG. 4 illustrating a track of the track and sprocket drive mechanism enlarged for magnification purposes;

FIG. 6 is a schematic side view of the track and sprocket drive mechanism in accordance with the present invention; and

FIG. 7 is a side view of an alternative embodiment of a drilling rig in accordance with the present invention.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

For purposes of the description hereinafter, the terms “upper”, “lower”, “right”, “left”, “vertical”, “horizontal”, “top”, “bottom”, “lateral”, “longitudinal”, and derivatives thereof shall relate to the invention as it is oriented in the drawing figures. However, it is to be understood that the invention may assume various alternative variations, except where expressly specified to the contrary. It is also to be understood that the specific devices illustrated in the attached drawings, and described in the following specification are simply exemplary embodiments of the invention. Hence, specific dimensions and other physical characteristics related to the embodiments disclosed herein are not to be considered as limiting.

With reference to FIG. 1, a drilling rig, denoted generally as reference numeral 1, that includes a highly controllable top drive carriage assembly 3 is illustrated. Drilling rig 1 may be used for vertical drilling, horizontal drilling, combination vertical/horizontal drilling, directional drilling, and various other drilling applications. Drilling rig 1 includes a mast base 5 and a mast 7 having a structural frame 9 extending from mast base 5. Mast base 5 and mast 7 are desirably transported to a drilling site on a flat-bed truck or any other suitable means for transportation. In addition, mast base 5 is anchored to the ground at the drilling site using any suitable anchoring means as are known in the art.

Structural frame 9 includes a first track 11 and a second track 13 extending along a length L thereof. First track 11 and second track 13 are spaced a distance D from each other and are positioned parallel to each other. As shown in FIGS. 5 and 6, first track 11 and second track 13 each include a plurality of bushings 15 equally spaced apart and attached to spaced apart track plates 17. Each of the plurality of bushings 15 has a hollow, cylindrical shape having a passage 16 therethrough and is manufactured from hardened steel. However, this is not to be construed as limiting the present invention as the bushings 15 may be of any suitable shape and may be manufactured from any material having sufficient durability.

Each of the plurality of bushings 15 is attached to the spaced apart track plates 17 by a bolt and nut arrangement 19 that passes through holes (not shown) provided in track plates 17 and through passage 16 in bushing 15. In addition, first track 11 and second track 13 may further include wear plates 21 positioned adjacent to the plurality of bushings 15 to prevent wear on track plates 17 as will be discussed in greater detail hereinafter. Bushings 15 are attached to track plates 17 in a pattern of motion desired. As shown in the figures, this pattern of motion is linear. However, this is not to be construed as limiting the present invention as the pattern may be non-linear depending on the application.

With reference to FIGS. 2 and 3 and with continuing reference to FIG. 1, drilling rig 1 also includes top drive carriage assembly 3. Top drive carriage assembly 3 includes a body 23 having a top drive drill head 25 and at least one sprocket arrangement 27 positioned thereon. Desirably and as shown in FIGS. 1 and 2, top drive carriage assembly 3 includes four sprocket arrangements 27A-27D. However, this is not to be construed as limiting the present invention as any suitable number of sprocket arrangements suitable to allow top drive carriage assembly 3 to travel along length L of mast 7 may be utilized.

Top drive drill head 25 is configured to be connected to the top of a drill string (not shown). Once a drill string is connected to top drive drill head 25, top drive drill head 25 provides a rotational drive force thereto. The rotational drive force is provided by a rotary hydraulic or electric motor (not shown).

In addition, top drive carriage assembly 3 is configured to move along length L of mast 7 by means of the four sprocket arrangements 27A-27D. Two of the sprocket arrangements 27A, 27B may be operatively engaged with first track 11 and two of the sprocket arrangements 27C, 27D may be operatively engaged with second track 13. More specifically, each of the sprocket arrangements 27A-27D has a plurality of teeth 29 configured to operatively engage the plurality of bushings 15 of either first track 11 or second track 13. The plurality of teeth 29 are formed in sprocket arrangements 27A-27D such that they engage the plurality of bushings 15 with a high degree of precision as shown in FIG. 6. Each sprocket arrangement 27 includes a round surface to one side of teeth 29 that acts as a roller to maintain a constant distance from the center of sprocket arrangement 27 to the track 11 or 13 with which the sprocket is engaged. Sprocket arrangements 27A-27D may be manufactured using a water-jet technique or any other suitable technique.

With reference to FIG. 4, and with continuing reference to FIGS. 1-3, each of sprocket arrangements 27A-27D is driven by a planetary drive assembly 31. Planetary drive assembly 31 includes a planetary gear arrangement 33, a hydraulic motor 35, and a brake 37. Each sprocket arrangement 27A-27D is driven by a separate planetary gear arrangement 33 driven by a hydraulic motor 35, such that sprocket arrangement 27A, 27B, 27C, or 27D rotates and operatively engages the plurality of bushings 15. This rotation of sprocket arrangements 27A-27D allows top drive carriage assembly 3 to move up and down along the length L of structural frame 9 of mast 7. As sprocket arrangements 27A-27D engage and move along the plurality of bushings 15, sprocket arrangements 27A-27D ride against wear plates 21. This prevents wear on track plates 17. Wear plates 21 and the bushings 15 are adapted to be easily removable and replaceable when either the wear plates 21 or bushings 15 are worn or fail.

In addition, since each sprocket arrangement 27A-27D is driven by a two speed planetary drive assembly 31 and a hydraulic motor 35 capable of smooth operation over a wide range of speeds, the drive mechanism of the present invention is highly controllable. A control panel 39 is provided at mast base 5. A canopy 40 is provided over control panel 39 to protect an operator from falling objects. Control panel 39 includes on/off switches 41 for each of four electrically-controlled hydraulic pumps (not shown) used to provide hydraulic power to drive the hydraulic motors 35. Any combination of positions of on/off switches 41 for the four electrically-controlled hydraulic pumps may be used to reduce hydraulic oil flow for more control, increase hydraulic oil flow for more speed, and/or avoid using a pump that is in need of repair. In addition, a potentiometer knob 43 and joystick control (not shown) are provided to control the speed and direction of hydraulic motors 35, thereby providing control of the speed of rotation and the direction of rotation of each of sprocket arrangements 27A-27D. The joystick control overrides potentiometer knob 43. This allows a user to set potentiometer knob 43 to a desired drilling speed allowing for hands-free operation, and then use the joystick control to override potentiometer knob 43 and take manual control of the drilling process. Accordingly, control panel 39 allows for precise control of the movement of top drive carriage assembly 3 along the length L of structural frame 9 of mast 7.

Top drive carriage assembly 3 further includes at least one, and desirably two, rollers 45 configured to move with top drive carriage assembly 3. Roller 45 is provided adjacent to an outer edge of the spaced apart track plates 17 of first track 11. Also, at least one, and desirably two, rollers 47 configured to move with top drive carriage assembly 3 are provided adjacent to an outer edge of spaced apart track plates 17 of second track 13. Rollers 45 and 47 are provided to prevent bowing so that the two track plates 17 of each of first track 11 and second track 13 remain parallel and equidistant to each other. In an alternative embodiment, rollers 45 and 47 can be replaced with additional sprocket arrangements 27 such that sprocket arrangements 27 are provided on both sides of first track 11 and second track 13. This alternative embodiment is illustrated in FIG. 7. First track 11 and second track 13 may be arranged differently to provide for a smaller overall mast dimension if desired.

In operation, mast 7 is raised onto mast base 5 such that it is substantially perpendicular to a surface of the ground. Next, an upper end of a drill string having a drill bit at a lower end thereof is coupled to top drive drill head 25 of top drive carriage assembly 3. Top drive drill head 25 provides a rotational drive force to the drill string such that the drill bit may be rotated to bore into the earth. The present invention may be used for several drilling methods including, but not limited to, rotary drilling by rotating the entire string, rotary hammer drilling by rotating the entire string, and directional drilling with a down-hole motor by rotating or holding the entire string. In addition, the drill string may be pushed downward to apply force to the drill bit by a downward movement of top drive carriage assembly 3 along first track 11 and second track 13 by the rotational engagement of sprocket arrangements 27A-27D with bushings 15 of first track 11 and second track 13. Once the entire length of the drill string has been bored into the earth, the upper end of the drill string is disengaged from top drive drill head 25 and top drive carriage assembly 3 is moved up along first track 11 and second track 13 by reversing the direction of rotation of sprocket arrangements 27A-27D. When top drive carriage assembly 3 reaches a desired height along length L of mast 7, a new section of drill pipe is coupled at an upper end to top drive drill head 25 and at a lower end to the upper end of the drill string. Top drive drill head 25 provides a rotational drive force and/or control of downward movement and force to the newly added piece of drill pipe such that the drill bit bores into the earth at the desired rate. Downward movement of top drive carriage assembly 3 along first track 11 and second track 13 is provided by the rotational engagement of sprocket arrangements 27A-27D with bushings 15 of first track 11 and second track 13. This process is then repeated, with new pieces of drill pipe being added to the drill string until the desired drilling depth is reached. The drilling rig of the present invention as shown in the figures allows for thirty (30) foot long pieces of drill pipe to be added to the drill string during each operation.

Accordingly, the present invention provides a drive mechanism for a top drive carriage assembly that cures the deficiencies of prior art drive mechanisms. For instance, the present invention provides a drive mechanism that is easier and/or cheaper to manufacture than a typical rack and pinion system. In addition, the present invention provides a drive mechanism for a top drive carriage assembly that is easier to service compared to a gear rack of a conventional rack and pinion drive mechanism due to size wearing elements and the ability to replace one bushing at a time rather than an entire gear rack.

Although the invention has been described in detail for the purpose of illustration based on what is currently considered to be the most practical and preferred embodiments, it is to be understood that such detail is solely for that purpose and that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover modifications and equivalent arrangements that are within the spirit and scope of the appended claims. For example, it is to be understood that the present invention contemplates that, to the extent possible, one or more features of any embodiment can be combined with one or more features of any other embodiment. 

1. A drilling rig comprising: a mast base; a mast comprising a structural frame extending from the mast base, the structural frame including a first track extending along the length of the structural frame and a second track extending along the length of the structural frame spaced from and parallel to the first track; and a top drive carriage assembly comprising at least one sprocket arrangement operatively engaged with one of the first track and the second track, wherein the first track and the second track each comprise a plurality of bushings equally spaced apart and attached to spaced apart track plates, and the at least one sprocket arrangement comprises a plurality of teeth configured to operatively engage the plurality of bushings such that the top drive carriage assembly moves along the length of the structural frame of the mast.
 2. The drilling rig of claim 1, wherein each of the plurality of bushings is attached to the spaced apart track plates by a bolt and nut arrangement.
 3. The drilling rig of claim 1, wherein each of the first track and the second track further comprises wear plates positioned adjacent to the plurality of bushings to prevent wear on the track plates.
 4. The drilling rig of claim 1, wherein at least one first roller configured to move with the top drive carriage assembly is provided adjacent to outer edges of the spaced apart track plates of the first track and at least one second roller configured to move with the top drive carriage assembly is provided adjacent to outer edges of the spaced apart track plates of the second track.
 5. The drilling rig of claim 1, wherein the at least one sprocket arrangement is driven by a planetary gear arrangement driven by a hydraulic motor.
 6. The drilling rig of claim 1, wherein the top drive carriage assembly includes four sprocket arrangements.
 7. The drilling rig of claim 6, wherein two of the sprocket arrangements are operatively engaged with the first track and two of the sprocket arrangements are operatively engaged with the second track.
 8. The drilling rig of claim 6, wherein each of the sprocket arrangements is driven by a separate planetary gear arrangement driven by a hydraulic motor.
 9. The drilling rig of claim 8, further comprising a control panel having four on/off switches, a joystick control, and potentiometer knob for controlling four hydraulic pumps.
 10. The drilling rig of claim 1, wherein the sprocket arrangement is manufactured using a water-jet technique.
 11. A drive mechanism for a top drive carriage assembly of a drilling rig comprising: a track comprising a plurality of bushings equally spaced apart and attached to spaced apart track plates; and at least one sprocket arrangement operatively engaged with the track, wherein the at least one sprocket arrangement comprises a plurality of teeth configured to operatively engage the plurality of bushings such that the sprocket assembly moves along the track.
 12. The drive mechanism of claim 11, wherein each of the plurality of bushings is attached to the spaced apart track plates by a bolt and nut arrangement.
 13. The drive mechanism of claim 11, wherein the track further comprises wear plates positioned adjacent to the plurality of bushings to prevent wear on the track plates.
 14. A method of drilling comprising: providing a drilling rig comprising: a mast base; a mast comprising a structural frame extending from the mast base, the structural frame including a first track extending along the length of the structural frame and a second track extending along the length of the structural frame spaced from and parallel to the first track, the first track and the second track each comprises a plurality of bushings equally spaced apart and attached to spaced apart track plates; a top drive carriage assembly comprising at least one sprocket arrangement operatively engaged with one of the first track and the second track; and the at least one sprocket arrangement comprises a plurality of teeth configured to operatively engage the plurality of bushings such that the top drive carriage assembly moves along the length of the structural frame of the mast; raising the mast onto the mast base such that it is substantially perpendicular to a surface; coupling an upper end of a drill string having a drill bit at a lower end thereof to a top drive drill head of the top drive carriage assembly; and providing a rotational drive force to the drill string by the top drive drill head such that the drill bit is rotated to bore into the earth.
 15. The method of claim 14, wherein each of the plurality of bushings is attached to the spaced apart track plates by a bolt and nut arrangement.
 16. The method of claim 14, wherein each of the first track and the second track further comprises wear plates positioned adjacent to the plurality of bushings to prevent wear on the track plates.
 17. The method of claim 14, wherein at least one first roller configured to move with the top drive carriage assembly is provided adjacent to outer edges of the spaced apart track plates of the first track and at least one second roller configured to move with the top drive carriage assembly is provided adjacent to outer edges of the spaced apart track plates of the second track.
 18. The method of claim 14, wherein the at least one sprocket arrangement is driven by a planetary gear arrangement driven by a hydraulic motor.
 19. The method of claim 14, wherein the top drive carriage assembly includes four sprocket arrangements.
 20. The method of claim 19, wherein two of the sprocket arrangements are operatively engaged with the first track and two of the sprocket arrangements are operatively engaged with the second track. 